1. Field of the Invention
The present invention relates to a process for the three step-multiplex control of electro-optical display arrangements having segment-like forward and back electrodes, through the intermediary of periodic pulse sequences which have six pulses within each control period, which can presently assume four different voltage levels, and wherein three of these pulse sequences are constantly applied to the back electrodes and the additional pulse sequences, in accordance with the measure of the display which is to be represented, are applied to the forward electrodes. The invention further relates to a circuit for effectuating the process for the three step-multiplex control.
For the control of liquid crystal display arrangements it is necessary that the display segments thereof be operated with alternating current since, otherwise, the life expectancy of the displays is extensively reduced. This requirement renders more difficult a multiplex control of liquid crystal displays and leads to a considerable increase in its circuitry requirements.
2. Discussion of the Prior Art
In a data sheet of the firm Shinshu Seiki Co. Ltd., dated July 15, 1977, under the heading "Specifications for Liquid Crystal Display LD-316", and in the periodical "Electronics" of July 5, 1979, page 141 under the title "Three-line multiplexing cut pin count of complex LCDs" by L. T. Reiss, there was disclosed a three step-multiplex control process which operates with four voltage levels and which evidences pulse sequences which are periodic step functions. For the control of displays, in particular of seven-segment displays, eight different pulse sequences are necessary for this process. Hereby, it is disadvantageous that for the generation of each pulse sequence it is necessary to provide a special switching circuit, which requires a significant manufacturing demand. In the utilization of microprocessors for the generation of the pulse sequences, this multiplicity of different pulse sequences leads to correspondingly high programming and storage requirements.